1. Field of the Invention
The invention is directed to a converter and method for determining a phase difference between two signals, particularly when the first signal is an excitation signal supplied to a resolver and the second signal is a response signal received from the resolver, so that the phase difference is equal to the shaft angle of the resolver.
2. Description of Related Art
Many applications require position sensing. One of the most robust, reliable, and often used position sensors is called a resolver. Resolvers require external excitation signals and output signal conditioning to obtain a usable signal (whether digital or analog) proportional to angular position.
Resolvers commonly use arc tangent integrated circuits for performing arc tangent conversion and resolver-to-digital integrated circuits. The available arc tangent integrated circuits perform arctangent conversion, but can operate only over a limited range, namely, from -90.degree. to +90.degree., exclusive. However, this limited range creates a major problem for devices such as resolvers that function over a full 360.degree. range.
Conventional resolver-to-digital circuits have a disadvantage in that they provide a discrete output instead of a continuous linear output, when the latter would be desirable for many purposes. Another circuit developed at NASA seeks to address this disadvantage, but requires precision analog circuitry and trigonometric identities to be implemented in the output signal conditioning circuit. Both of these tend to be noise-sensitive, require precision components, require gain and phase matching, drift with temperature, and are expensive to implement.